1. Field of the Invention
The field of art which the claimed invention pertains is the catalytic cracking of hydrocarbons. More specifically, the claimed invention relates to a process for the passivation of contaminating metals on a fluidized cracking catalyst.
2. Description of the Prior Art
There are a number of continuous cyclical processes employing fluidized solid techniques in which carbonaceous materials are deposited on the solids in the reaction zone and the solids are conveyed during the course of the cycle to another zone where carbon deposits are at least partially removed by combustion in an oxygen-containing medium. The solids from the latter zone are subsequently withdrawn and reintroduced in whole or in part to the reaction zone.
One of the more important processes of this nature is the fluid catalytic cracking process for the conversion of relatively high-boiling hydrocarbons to lighter hydrocarbons boiling in the heating oil or gasoline (or lighter) range. The hydrocarbon feed is contacted in one or more reaction zones with the particulate cracking catalyst maintained in a fluidized state under conditions suitable for the conversion of hydrocarbons.
A common problem in the fluid catalytic cracking process is the gradual deterioration of the catalyst due to the deposition on the catalyst of metal contaminants contained in the hydrocarbon feed, such as nickel, vanadium and iron. These deposited metal contaminants increase the production of hydrogen, undesired light gases and coke at the expense of the highly desirable gasoline. A further disadvantage of high hydrogen and light gas yield is that a larger capitol investment is required in equipment needed to deal with the large volume of gases.
The art teaches many techniques for dealing with these undesirable metal contaminants. Such techniques can be divided into two broad categories, one being the passivation of the contaminants by reacting the catalyst with a passivating agent, which converts the metal contaminants to a relatively innocuous form, and the other being the physical removal of the contaminants from the catalyst. Examples of techniques falling within the former category are as taught or claimed in U.S. patent publication Nos. 2,758,097 (reaction with phosphorous pentoxide); 3,711,422 (reaction with an antimony compound); and 4,025,458 (reaction with chemical complexes containing antimony). Examples of techniques falling within the latter category are as taught or claimed in U.S. patent publication Nos. 3,252,918; 3,324,044; 4,013,546; and 4,014,815.
U.S. patent publication No. 2,981,676 discloses that a metals contaminated cracking catalyst can have its activity and selectivity improved by adding to it at appropriate conditions a small amount of alkali or alkaline earth metal oxide. The preferred amount is stated to be between about 0.05% and 0.5% by weight. This reference warns against an alkali concentration above about 0.5 wt. percent because of concentrations that high being "known to adversely affect the activity and selectivity of cracking catalysts".
I have found a process for passivating an undesired metal contaminant on a fluid cracking catalyst for use in a fluidized cracking system by reaction with a lithium compound in concentrations for exceeding the ranges heretofore thought practicable for alkali metals.